2,4,6-Triphenylpyrylium thiocyanate

A novel method for the synthesis of thiocyanates amounts to the overall conversion RNHj - RSCN. The amine is allowed to react with 2,4,6-triphenylpyrylium thiocyanate and the resulting pyridinium thiocyanate is pyro-lysed at 180—200 °C. The point is made that this method is safer than the classical diazotization-substitution sequence for bringing about this conversion (illustrated recently for 3-aminothiophens, to give 3-thienyl thiocyanates and selenocyanates ). 

A new synthesis of thiocyanates from aliphatic amines (Scheme 46) utilizes the readily available 2,4,6-triphenylpyrylium thiocyanate (80). The intermediate l-substituted-2,4,6-triphenylpyridinium thiocyanates (81) are smoothly pyrolysed into the corresponding thiocyanates (82) in excellent yields. These promising syntheses complement those available in the aromatic amine series via diazotization. 

Continuation of the work reported last year on the conversion of 2,4,6-triphenylpyrylium salts into the corresponding 2,4,6-triphenylpyridiniums has yielded additional synthetically useful procedures. Examples are the conversion of alkyl, aryl, and heteroaryl primary amines into iodides,esters, " and thiocyanates and the production of carbodi-imides from amidrazones, as outlined in Scheme 34. ... 

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